Question about best fit - recomp

[pcdmisstudent]

Howdy

Ive got a question about best fit recomp constructions (specifically for construction of circles).
I read here on the forum that best fit recomp only recompensates for the active tip when constructing the element.

So lets say ive got a star probe and the tips on the star has different diameters, (lets say Ø2mm east-west, Ø4mm north-south).
I now measure a bunch of points with each of these tips and construct a circle out of the points.

I have Ø2mm tip as active tip during construction, will it not compensate for the Ø4 tips too?

[JEFMAN]

I would say the best way understanding compensation is trying !!!!!
Construct the BF circle from hits, construct the BFRE circle from hits (so you don't change anything to the measurement !), and look at the form... You will find the answer !

BFRE calculate a feature from centerballs hits, and then apply a radius compensation. So I believe it can't apply different radii, because the feature is calculated first.
In your case, you can measure some surface points around the circle (so the compensation is right), or just construct the circle from hits, but don't use BFRE.

[AndersI]

I have a faint memory of having tested this quite a while ago, and it worked - maybe the compensation problem was a long time ago, in a PC-DMIS version far, far away...

I don't see it in experiments offline, at least. Neither on a measured circle with a star probe (1mm and 5mm tips) or a constructed circle from individual vector points.

Re-constructing a new circle from the circle .HITs also gives the same result as the original circle.

[Matthew D. Hoedeman]

I have a faint memory of having tested this quite a while ago, and it worked - maybe the compensation problem was a long time ago, in a PC-DMIS version far, far away...

I don't see it in experiments offline, at least. Neither on a measured circle with a star probe (1mm and 5mm tips) or a constructed circle from individual vector points.

Re-constructing a new circle from the circle .HITs also gives the same result as the original circle.

you sure that wasn't from a learned circle with tip changes between hits of the feature? wasn't that the issue? it used the last active tip for all comp?

[NinjaBadger]

That was the issue but I believe that's what he means by 'a measured circle'.

[Matthew D. Hoedeman]

yeah, but a constructed feature (OP) isn't the same as a measured circle, just pointing it out...

[AndersI]

I tested a measured circle with (star)tip changes between the points (1mm and 5mm tips) - worked perfectly offline.
I also tested a constructed circle, from vector points taken with different tips - worked perfectly offline.
I don't have access to a cmm very often, so I'll let others test out in the wild...

[tking]

I did try this out (long ago) with 3.7. Same tip is OK, diff tips NOT is my recollection. Vector points with diff tip and constructed circle with recomp gave an incorrect dia. I did it with a large size diff between the tips and got wide diff in dia and it would change with the last point recalled in the construction.

TK

[AndersI]

A long time ago, in a PC-DMIS far, far away...

[Matthew D. Hoedeman]

not so long ago.... still using that here.

[tking]

Rocks were weapons long, long ago and still are today Running 2015 now.